Travelling within Bulgaria can be an exciting experience, but there are a few guidelines that should be followed to ensure safety and avoid getting ripped off.
Corruption is still an issue in Bulgaria. They joined the EU in 2007, and it will take some time for people to get into the modern way of doing things. As such, some careful consideration should be taken before just taking off into the countryside.
If you do decide to rent a car be aware that road conditions in Bulgaria are tragically bad. They are getting better with the recent influx of cash from the EU, but it will take 10 or more years to address the worst of them. It is NOT recommended that you drive at night because of the number of dangerous potholes. Also be aware that traffic police can stop you for what are often ridiculously trumped-up charges, and are notoriously corrupt and known for making up things on the spot to get you to pay them in order to be let on your way.
There is an example of one American who took the 3 hour drive from Sofia to Varna and spent 18 hours in transit. He was pulled over a total of 14 times and had to negotiate monetarily for each “offense”. Driving like a saint is apparently not a guarantee for avoiding getting pulled over. And while corrupt traffic police are becoming less and less of an issue, driving is generally NOT recommended. You are better off taking public transportation or getting a taxi.
Despite this, rental agencies are all over the country and you can rent cars for your specific needs. Just be warned that driving here carries its own set of dangers.